The present invention relates generally to methods for forming filaments from a resin and more particularly to methods for processing a resinous organosilicon polymer to prepare it for melt spinning into a filament.
Certain resinous organosilicon polymers are useful as precursors for forming ceramic fibers having a composition consisting essentially of silicon and at least one of nitrogen and carbon. These ceramic fibers are useful, for example, in composite, high temperature-resistant materials, e.g., materials made into jet engine parts.
The resinous organosilicon polymer typically contains silicon, hydrogen, nitrogen and carbon, with oxygen present as an impurity. It may also contain certain additives, such as chlorine, boron, titanium or aluminum. This resin is typically processed into a fiber by melting solid resin and then melt spinning the molten resin in a conventional spinning device called a spinnerette, to form one or more filaments which are gathered into a fiber, and the fiber is wound around a spool or reel. The fiber is subjected to a cure process following which the cured fiber is subjected to a pyrolyzing operation which typically drives off the hydrogen and some of the nitrogen, silicon, carbon and oxygen as gas or vapor, to produce the ceramic fiber.
A more detailed description of a process for forming a ceramic fiber from a resinous organosilicon polymer is contained in an article by LeGrow et al., "Ceramics From Hydridopolysilazane", Am.Ceram.Soc.Bull., 66[2]: 363-67 (1987), and the disclosure thereof is incorporated herein by reference.
A procedure which has been utilized for producing a molten resinous organosilicon polymer prior to melt spinning is to take solid resinous organosilicon polymer, the form in which that polymer is usually provided by the manufacturer thereof, break or crush the solid polymer into smaller pieces, and feed the smaller polymer pieces to a heated, screw type extruder, the output from which serves as the feed material to the melt spinning operation.
An alternative procedure involves compacting the smaller polymer pieces into a solid rod, typically employing pressure and elevated temperature and then mechanically forcing the solid rod against a heated plate to form molten polymer for melt spinning.
In a further alternative procedure, heat is applied to the polymer in a closed container to effect melting. The container of molten polymer then serves as a reservoir of feed material for the spinning operation.
The above-described procedures have been employed successfully in connection with organic polymers subjected to melt spinning, but they have several drawbacks when employed on resinous organosilicon polymers.
When resinous organosilicon polymer is at a temperature above its melting point for an extended period of time there is a danger that it will undergo heat degradation causing a loss of properties which are desirable in the subsequent processing and end uses. The danger of heat degradation is present when molten resinous organosilicon polymers are prepared employing the procedures described in the preceding paragraph. In addition, those procedures can cause undesirable air entrainment in the resinous organosilicon polymer or otherwise contaminate it which eventually results in poor physical properties in the ceramic fiber made from the resinous organosilicon polymer.